If I am only concerned about the files in my MBP, is hfs-windows all I need?
On my iPad, I only use files stored in Drobox. As for my iPhone, I just store the photos in the phone. One strange thing is that about 8 months ago, Apple store genious said that my iCould storage was almost full. He could not back it up. However, when I sent it to the store to exchange the battery a month ago, the genious said that all the photos and videos have been backed up to iCloud. How do I check?
Once my Mac is gone, can I just plug in my iPhone/iPad to a Windows PC and sync/store the photos and videos from these iOS devices to the PC?
Do you have an external hard drive? Just format it to exFAT instead of HFS and copy all your files to it. Then you can access them on your PC. Then you can reformat the SSD when you get the Windows computer and use it as a boot drive or secondary drive. Moving the files back to it if you so choose.
You can always login to your account on iCloud.com to see if your Photos and Videos are there. They should be if you have the appropriate
iCloud options enabled. When looking at iCloud options look at open Backup to see the status.
Yes you can store the photos and videos on the PC. Not sure about syncing but the "Import Pictures and Videos" can transfer new photos and videos. Once the iPhone is properly installed via iTunes.
Photos: If you are using Photos to organize your pictures. You'll want to find a means of exporting them on the Mac first. Then transfer those instead of the Photos library. iCloud is capable of syncing them but you won't have any folders, just a mass of pictures and videos. This is may be the biggest challenge.
If you want to manage pictures over the cloud and have them sync. The last I checked Adobe Lightroom is the best candidate it's a little costlier but you also get Photoshop with the subscription. iCloud syncing with Windows isn't good if you do a lot of library management. Google Drive added Google Photos support and it supposedly works with Windows 10 Photos app. I couldn't say how well and if you get an editable album structure or not. This wasn't and option when I last investigated this. There might be smaller companies but who knows how long they will last. You'll want something which also works with Android since you are considering that move as well. Which Lightroom and Google Photos do.
I couldn't say what is best for Linux. Besides setting a HDD to exFAT for moving your files and reformatting the SSD for Linux instead of Windows.